In an electrophotographic image forming apparatus, power supplied to a motor that drives a drum-like image carrying member is adjusted, and thereby the rotation speed and the rotation direction (orientation) of the image carrying member is controlled.
It is known, for example, that the motor can be controlled by a feedback control for adjusting the power supplied to the motor in a direction where a difference between a target position and a measured position (detected position) of the motor is reduced. The target position is obtained by counting edges of a reference pulse signal. In addition, the measured position is obtained by counting edges of an encoder pulse signal that is synchronized with the rotation of the motor. The encoder pulse signal is output from an encoder attached to the motor.